This invention is generally directed to toner compositions and developer materials containing such compositions, as well as the use of these materials in electrostatographic imaging systems, particularly those systems wherein the photoresponsive device utilized has been charged negatively. More specifically, the present invention is directed to developing compositions wherein the toner component is charged positively by certain charge control additives which toner compositions having improved particle to particle uniformity, fast admix charging, narrow charge distributions, improved humidity stability, improved thermal stability, improved resin dispersibility, and improved carbon black dispersion.
The utilization of charge enhancing additives are known in the prior art, these additives being used primarily for the purpose of imparting a positive charge to the toner composition. There is described for example in U.S. Ser. No. 911,623, filed on June 1, 1978, developing compositions comprised of toner particles, carrier particles and as a charge control additive an alkyl pyridinium halide. Also there is disclosed in U.S. Pat. No. 3,893,935 the use of certain quaternary ammonium compounds as charge control agents for electrostatic toner compositions. According to the disclosure of this patent certain specific quaternary ammonium compounds when incorporated into toner compositions were found to provide a toner which exhibited relatively high uniform and stable net toner charge when mixed with a suitable coated carrier. U.S. Pat. No. 4,079,014 contains a similar teaching with the exception that a different charge control agent is utilized namely a diazo type material.
While some of the above developing compositions are suitable for certain purposes, their solubility in water causes difficulties in uniformly dispersing such materials in toner formulations comprising toner resins and carbon black. Further, some of the prior art charge enhancing additives when incorporated into toner compositions migrate to the toner surface at high relative humidity, and as it is very difficult to disperse or dissolve such compound uniformly in the toner composition there results particle to particle non-uniformity and in some instances wide distribution of electrical charge which is not desired.
There continues to be a need for developing compositions which can be used in imaging systems wherein the photoresponsive member is charged negatively, and more specifically, there continues to be a need for improved toner compositions which are positively charged and contain therein charge enhancing additives which are soluble in organic materials and which are humidity insensitive. Additionally there continues to be a need for toner compositions which will rapidly charge new uncharged toner being added to a developing composition comprised of charged toner particles and carrier particles, which toners are humidity insensitive, and wherein the charge enhancing additive is compatible with the toner resin.